As one method of suppressing a magnetizing inrush current in a transformer, there has been known a phase controlled energizing method of energizing a circuit breaker in a predetermined phase of a three-phase power supply. The present invention relates to a transformer inrush current suppression apparatus using the phase controlled energizing method.
This type of a conventional transformer inrush current suppression apparatus such as, for example, a transformer inrush current suppression apparatus disclosed in Patent Document 1 operates as follows. The transformer inrush current suppression apparatus lowers phase voltages of respective phases by using step-down means for lowering phase voltages of a three-phase transformer so that the phase voltages become suitable for input signals to an optimum energizing phase calculating apparatus serving as an electronic apparatus, where the phase voltages change transiently, and finally become zero when the three-phase transformer is de-energized. Then, using residual flux calculating means, the transformer inrush current suppression apparatus calculates residual fluxes in an iron-core of the three-phase transformer by time-integrating inputted signals of lowered three phase voltages. Using energizing phase calculating means, the transformer inrush current suppression apparatus calculates optimum energizing phases for the three phases, which do not cause the magnetizing inrush current and are different from each other, by using an equation derived from a relational equation among a magnetic flux at a time of the energization, an energizing phase and a residual flux. Calculation results of the optimum energizing phases are used as output signals from the optimum energizing phase calculating apparatus, and the output signals are used as energizing phase signals for a phase controlling apparatus for the circuit breaker. The circuit breaker is energized at the respective phase voltages individually.
In addition, a transformer inrush current suppression apparatus disclosed in Patent Document 2 sets one of the three phases to a first closing phase. A phase of zero degree of a standard phase is used as a reference point, and residual fluxes of the remaining two phases are assumed to be zero. Regarding each of the remaining two phases, the transformer inrush current suppression apparatus calculates a closing phase when an energization flux error becomes minimum, by associating an interpole voltage for each of the remaining two phases with a previously obtained pre-arc characteristic and a previously obtained closing time variation characteristic of the three-phase circuit breaker, and sets calculated closing phases to target closing phases for the remaining two phases. Each of the interpole voltages for the remaining two phases is a difference between a voltage on a power-supply-side and voltage on a transformer-side. The interpole voltages for the remaining two phases are smaller than a voltage value of an interpole voltage for the first closing phase, which is a difference between a voltage of the first closing phase on power-supply-side and a voltage of the first closing phase on a transformer-side of the first closing phase. The transformer inrush current suppression apparatus sets a target closing timing for each of the remaining two phases to a time interval obtained by adding a time interval from the reference point to the target closing phase of each of the remaining two phases, and a delay time previously set based on a time interval during which a direct-current component of the residual flux of each of the remaining two phases becomes zero after energization of the first closing phase. The delay time corresponds to an integral multiple of a time cycle of the three-phase power supply. Upon inputting a closing command, the transformer inrush current suppression apparatus closes the remaining two phases at the target closing timings, respectively.